Enhancement of Wear Behavior of Base Oil by Reduced Graphene Oxide Additives

Jankhan Patel¹, Gavin Pereira ², Doug Irvine ³, Amirkianoosh Kiani ^1*,

¹ Silicon Hall: Micro/Nano Manufacturing Facility, Faculty of Engineering and Applied Science, University of Ontario Institute of Technology (UOIT), Ontario, Canada

²Kinetrics Inc., 800 Kipling Ave., Toronto, ON, M8Z 5G5

³Petro-Canada Lubricants Inc., 2310 Lakeshore Road West, Mississauga, Ontario, Canada L5J 1K2

^* Corresponding author: amirkianoosh.kiani@uoit.ca

INTRODUCTION: Industrial development brought a revolution in the manufacturing processes however; friction and wear are damaging efficiency and sustainability of the industry, which leads researchers to improve lubrication capabilities. Lubricants are keeping two mating surfaces isolated from each other by creating a thin layer between them to avoid metal to metal contact. In past, many researches have been proposed to improve lubricants by adding nano additives, which can enhance properties like extreme pressure, anti-wear, anti-friction, corrosion inhibitor, anti-foam and viscosity. As per the application of the lubricant different additives can be added in to the base oil and desirable properties can be achieved. In this study, three different forms of reduced graphene oxide(rGO) are introduce as a nano additives to enhance lubrication wear resisting property. Graphene is consider as strongest material ever measured, when it is in perfect crystalline form which can uphold its wear resisting characteristic as an additive [1]. To analyze the effect of rGO on the base oil, four-ball wear test and viscosity tests were performed. Having a difference in the physical and chemical properties of an additives, can leads to sacrifice some of it’s important properties like viscosity and viscosity index. The findings of this study indicate that reduced graphene oxide can have promising results as anti-wear additives, which can be used by industry to eliminate damage in economy and sustainability.

METHODS: Graphene oxide (GO) can be reduced using different methods such as thermal reduction, chemical reduction and multistep reductions via modified hummers method [2]. Three forms of rGO were produced by modified hummers method having different synthesis time and filtration. In this experiment, 99% pure base oil was used, provided by Petro Canada (200 Neutral medium HT). Samples were prepared using 0.05%w/w concentration using a mixture for 30min and ultrasonicated for 20 minutes. To analyze the structures of three rGOs used in this project via transmission electron microscopy (TEM), epoxy resin was used to mold rGO in to a bullet shape and then sliced them in to 90nm thin sheets using a diamond knife, which can uphold capability to investigate under TEM.

Table 1 – Materials density and wear scar diameter (WSD), (error: ± 0.12 mm)

RESULTS & DISCUSSION: Due to different synthesis time and filtration method, all three materials have different density values as shown in Table-1. Material-1 has the lowest density (highest porosity) compare to other two materials. To check the effect of all three additives on wear preventive properties, four-ball test was performed for 60min on each sample as per ASTM D4172 standard. Three balls were suspended at the bottom and 240N dead load was subjected on the fourth ball on top and ran at 250 RPM. Each test was performed twice with a same condition and average

results were considered along with that, before each test samples were sonicated for 20 minutes. Results shown in Table-1 indicates that material-1 is having lowest wear scar diameter compare to material-2 and 3 with respect to the base oil. As shown in Figure-1 TEM images were taken at 2µm using FEI Tecnai 20 transmission electron microscope (TEM). In addition, image processing shows that Material-1 has highest number of layers, material-2 has moderate and material-3 has least.

Figure-1 TEM images of three forms of rGO

To analyze the effect of these additives on lubricant’s key properties, kinematic viscosity and viscosity index were measured as per ASTM D445 and ASTM D2270. Results shown in Fig-2 indicates that there is no enormous difference in the viscosity and viscosity index on the materials having additives in comparison with the base oil (control sample) which proves that because of these additives lubricant will not sacrifice temperature resistive characteristic.

Figure 2 - Kinematic viscosity

CONCLUSION:As three forms of rGO were prepared using modified hummer’s method and tested at 0.05%w/w concentration, which showed excellent effect on reducing steel-steel direct contact and uphold wear properties of the material without affecting lubricant’s key property. Out of all three forms of rGO, material-1 having least density and more number of particles helps to improve the sustainability and wear ability of the mating parts. The findings in this project can direct to new generation of lubricant enhanced by graphene-based nanomaterials. For future study, friction coefficient can be investigated with respect to time, load and speed; also higher concentration of additives can be checked.

REFERENCES:

[1] W. J. a. H. L. a. K. P. Evans, "Thermal conductivity of graphene ribbons from equilibrium molecular dynamics: Effect of ribbon width, edge roughness, and hydrogen termination," Applied Physics Letters, vol. 96, p. 203112, 2010.

[2] R. S. R. Sungjin Park, "Chemical methods for the production of graphenes," Nature Nanotechnology, vol. 4, pp. 217-224, 2009.